Dedifferentiation of Human Terminally Differentiating Keratinocytes into Their Precursor Cells Induced by Basic Fibroblast Growth Factor

Reprogramming differentiated cells toward stem cells may have long-term applications in stem-cell research and regenerative medicine. Here we report on the dedifferentiation of human epidermal keratinocytes into their precursor cells in vitro with basic fibroblast growth factor (bFGF) but not external gene intervention. After incubation of human terminally differentiating keratinocytes, some of the surviving keratinocytes reverted from a differentiated to a dedifferentiated state, as evidenced by re-expression of biological markers of native keratinocyte stem cells (nKSCs), including β(1)-integrin, CK19 and CK14. Moreover, these dedifferentiation-derived KSCs (dKSCs) showed an ability for high colony formation correlated with cell cycle analysis showing a marked accumulation in S phases, acquired a similar regional distribution of both α(6)-integrin and CD71 expression at the ultrastructural level, and had a increased proliferative capacity by releasing telomerase from nucleolar sites to nucleoplasmic distribution. However, on comparing dKSCs with nKSCs, 2 points seem noteworthy: (1) the proportion of transit amplifying cells in dKSCs treated with bFGF is much higher than that in nKSCs and (2) regional differences exist in the subcellular localization of telomerase in nKSCs and dKSCs. Most nKSCs showed a prominent nucleolar concentration of human telomerase reverse transcriptase expression, whereas most dKSCs showed a more diffuse intranuclear distribution of telomerase or even signal depletion at nucleoli relative to the general nucleoplasm. These results indicate that bFGF could induce the terminally differentiating epidermal keratinocytes to convert into their precursor cells, which offers a new approach for generating residual healthy stem cells for wound repair and regeneration.